1. Field of the Invention
The present invention relates to a universal motor, and more particularly, to a bracket assembly of a universal motor capable of reducing the number of components and facilitating an assembly operation.
2. Description of the Conventional Art
Generally, a universal motor is being widely used as a motor for a washing machine or a motor for a cleaner since a driving torque is great, an rpm in a no-load state is high, a fast rotation is easy, and both a direct current and an alternating current are used as a power source.
The universal motor is largely divided into a housing type and a frame type according to an appearance thereof. The former shields a penetration of foreign materials by installing a stator in a housing, and the latter enhances a light emitting effect by exposing a stator to outside.
FIG. 1 is a partially-cut perspective view showing one example of a universal motor in accordance with the conventional art.
As shown, the universal motor comprises: a stator 100 having a winding coil therein; a rotor 200 rotatably inserted into the stator 100; a rotation shaft 300 penetratingly-coupled to the rotor 200; a front bracket 400 formed as a certain shape and coupled to a front surface of the stator; a rear bracket 500 formed as a certain shape and coupled to a rear surface of the stator 100; a commutator 600 coupled to the rotation shaft 300 so as to be positioned at the rear bracket 500, for converting a phase of a supplied current; a brush assembly 700 mounted at the rear bracket 500, for supplying a current to the commutator 600; bearings 310 respectively mounted at the front bracket 400 and the rear bracket 500, for supporting the rotation shaft 300; and a tachometer 800 mounted at the rear bracket 500, for detecting a rotation speed of the rotation shaft 300.
FIG. 2 is a perspective view showing the rear bracket, a brush assembly mounted at the rear bracket, and a tachometer.
As shown, the rear bracket includes: a base portion 510 of a plate shape having a certain area; a bearing mounting portion 520 protruded in the base portion 510 as a cylindrical shape, for insertion-fixing the bearing 310 thereto; mounting portions 530 extension-protruded at one surface of the base portion 510 with the same interval as a certain shape; and reinforcing portions 540 protruded at one surface of the base portion 510 as a certain shape. A plurality of first screw holes 550 for coupling the stator 500 are formed at the edge of the base portion 510, and second screw holes 560 for mounting the brush assembly are formed at both sides of the bearing mounting portion 520. Two second screw holes are formed per one side, so that the total number of the second screw holes 560 is 4. Also, a through hole 570 is formed in the middle of the bearing mounting portion 520, and an extension portion 580 of a certain shape is respectively formed at both sides of the bearing mounting portion 520. The extension portion 580 is respectively provided with third screw holes 590 for mounting the tachometer.
The rear bracket 500 is formed of Al, a non-conductive material, and is fabricated by a molding.
The brush assembly 700 includes: a brush holder 710 having fixing portions 712 extendingly formed at both sides of a square holder body portion 711; a brush 720 inserted into the brush holder 710; a spring 730 inserted into the brush holder 710 and supporting the brush 720; and a cover 740 coupled to the brush holder 710 and supporting the spring 730.
The brush assembly 700 is fixed as the fixing portion 712 of the brush holder is positioned at the base portion 510 of the rear bracket and screws 750 are respectively coupled to the screw holes 713 formed at the fixing portion 712 and the second screw holes 560. The brush 720 is in contact with the commutator 600 coupled to the rotation shaft 300 by an elastic supporting of the sprig 730.
Two brush assemblies 700 are mounted at the rear bracket 500.
The tachometer 800 includes: a body portion 810 of a certain shape; fixing portions 820 respectively extended at both sides of the body portion 810; and screw holes 830 respectively formed at the fixing portions 820.
The tachometer 800 is fixed to the extension portion as the fixing portion 820 is positioned on an upper surface of the bearing mounting portion 520 in a consistent state with the extension portion 580 and screws 840 are respectively coupled to the screw holes 830 formed at the fixing portion 820 and the third screw holes 590 formed at the extension portion 580.
Operation of the universal motor is as follows.
First, when a power source is supplied to the motor, a current is applied to the brush 720 of the brush assembly through a stator winding coil. While a phase of the current applied to the brush 720 is continuously changed by the commutator 600, the current is applied to a rotor winding coil. By an interaction between a flux formed by the current applied to the stator winding coil and a flux formed by the current applied to the rotor winding coil, the rotor 200 is rotated. A rotation force of the rotor 200 is transmitted to another component through the rotation shaft 300.
The bearings 310 mounted at the front bracket 400 and the rear bracket 500 support the rotation shaft 300, and a rotation speed of the rotation shaft 300 is detected by the tachometer 800.
In fabricating the universal motor, it is important to maximize the motor efficiency and to optimize the structure thereof. When the motor efficiency is increased, a consumption power is decreased. Also, when the structure of the universal motor is optimized, the number of components is reduced and a fabrication process is simplified thereby to reduce a fabrication cost.
However, in the conventional universal motor, the brush assembly 700 mounted at the rear bracket 500 is composed of the brush holder 710, the brush 720, the spring 730, and the cover 740, and the brush assembly 700 is mounted at the rear bracket 500 by two screws 750. According to this, the number of components is relatively great and the structure is complicated. Also, the number of processes for mounting the brush assembly 700 to the rear bracket 500 is great, thereby lowering an assembly productivity and increasing a fabrication cost.
Also, when the tachometer 800 for detecting a rotation speed of the rotation shaft 300 is mounted at the rear bracket 500, the extension portion 580 has to be provided to the rear bracket 500 and the tachometer 800 has to be coupled by two screws 840. According to this, the structure is complicated and the number of assembly processes is relatively great, thereby lowering an assembly productivity and increasing a fabrication cost.
Additionally, when the rear bracket 500 is coupled to the stator 100, it is difficult to make a concentricity between the inner hole of the stator 100 for inserting the rotor 200 and the bearing mounting portion 520 of the rear bracket for coupling the bearing 310 be consistent with each other. According to this, an assembly productivity is significantly lowered.
Besides, heat generated from the brush 720 constituting the brush assembly 700 is not quickly emitted to the outside, thereby lowering the motor efficiency.